Electronic components are typically assembled into complex circuits by mounting them on printed circuit boards. These printed circuit boards are usually flat nonconductive boards with one or more layers of a conductive material such as copper fixed on or in the printed circuit board. The layers of copper are etched or otherwise formed to specific shapes and patterns in the manufacturing process, such that the remaining conductive copper traces are routed to connect electrical components to be attached to the printed circuit board.
It is not uncommon for printed circuit boards such as these to have copper layers on both a top and bottom side of the circuit board, but also several layers of copper traces or patterns sandwiched at various depths within the circuit board itself. These traces allow greater flexibility in circuit routing, and usually allow designing a more compact circuit board for a particular circuit than would otherwise be possible. The various layers are sometimes dedicated to particular purposes, such as a ground layer that only serves to distribute ground or signal return connections to various components.
Circuit board layers that serve to connect components to other components often must connect to components attached to a different layer (top or bottom), or such layers must be attached to each other at selected points, requiring use of what are commonly known as vias. These vias typically are essentially small conductive plated-through hole elements oriented perpendicular to the top and bottom surfaces of a circuit board that extend through at least two conductive layers of the circuit board, and that electrically connect circuit traces on at least two of the conductive layers to each other. These vias may be filled with solder during the solder printing process of printed circuit board fabrication, if a method is used that enables application of sufficient solder to fill the hole.
Connection of components such as through-hole mounted (THM) components or solder-connected shields to the printed circuit board can also require a relatively large amount of solder to ensure a reliable connection, and therefore ideally will use more solder than a typical printed circuit board printing process will provide. Some ceramic components such as ball-grid arrays (BGAs) or other surface mount devices may also benefit from more solder than is typically ideal for most of the rest of a printed circuit board, further evidencing a need for application of a relatively large amount of solder to selected areas of a circuit board.
Solutions to this need for additional solder on some certain areas of printed circuit boards typically involve increasing the density of the solder applied to all areas of the board in the solder printing process, or use of various types of stencil to apply additional solder to the board. But, because of the fine pitch of interconnects and component connection pads on many printed circuit boards, application of a relatively large amount of solder throughout a circuit board is not desirable because it tends to cause solder bridging between traces and pads on the circuit board. Similarly, use of thick stencils requires a spacing of typically 4 mm around the area to which solder is to be applied, can impact other surface mount components on the circuit board, and is rather limited in the amount of solder than can be applied. Overprint stencils are further limited in the solder volume that can be applied, and so are also undesirable for many applications.
All current known solutions to the need for additional solder on certain areas of a printed circuit board involve the printing process, and are limited by the technology of the solder printing apparatus which was not designed to vary the amount of solder printed across a circuit board. Use of stencils and extra-thick solder application are not appropriate solutions for applications involving fine pitch circuit traces and pads, or for many surface mount technology applications.
What is needed is a technology enabling selective application of an amount of solder greater than is normally applied in a solder printing process to selective areas of a printed circuit board.